This invention relates to an apparatus for measuring the length of weft yarn for a loom, in which the weft yarn supplied from the weft yarn supply unit is wound on a winding surface for length measurement and the weft yarn whose length has been measured is stored provisionally in the wound state so as to be pulled out at the time of subsequent weft insertion.
In a shuttleless loom in general, and particularly in a jet loom, an apparatus is provided for measuring a length.of weft yarn corresponding to one weft inserting operation and provisionally storing the measured length of weft yarn. According to the apparatus of this type so far proposed in the art, the weft yarn supplied from the weft yarn supply unit is wound for length measurement and the weft yarn whose length has been measured is provisionally stored in the wound state so as to be subsequently pulled out for weft insertion.
With this winding type apparatus, the weft yarn is wound on the yarn winding surface of a yarn length measurement element such as drum, and the length of the weft yarn wound on said surface as well as transfer thereof in the weft yarn inserting direction is controlled by at least a pair of weft yarn latching pins adapted for emerging from and receding into the inside of the yarn winding surface. The weft yarn is usually passed through a yarn supply pipe adapted for rotation relative to the measurement element, and is wound on the winding surface of the element.
It is to be noted that, when only one kind of weft yarn is supplied from only one supply source and inserted for forming a woven cloth, only one weft yarn length measurement unit will serve the purpose. However, when the weft yarns are supplied from two or more supply units, it is necessary to provide a number of weft yarn length measurement units equal to the number of said supply units. For example, when two weft yarns are supplied alternately from two weft yarn supply units, two measurement units are used. In this case, the supply speed of each weft yarn or the winding speed of each weft yarn on the measurement element of each unit is one half the winding speed for the case of using only one measurement unit (hereafter referred to as usual winding speed) so that the length of each weft yarn is measured once per two weft inserting operations, with the weft yarns being laid down or inserted alternately. This type of weft insertion is resorted to not only when supplying two weft yarns of different color but when supplying the same kind of weft yarn from two weft yarn supply units with a view to realizing a cloth of uniform quality consisting of one kind of weft yarn. The art of supplying the same kind of weft yarns from plural weft yarn supply units is known as mixing.
The aforementioned pattern of weft insertion may be applied to cases where three or more weft supply units are used. Thus, when three weft yarn supply units are used, the winding speed of each yarn is one third the usual winding speed, and a length of each weft yarn corresponding to one weft insertion (hereafter referred to as preset length) is measured per three weft inserting operations with the thus measured lengths of the three weft yarns being laid down successively. When there are four weft yarn supply units, the winding speed of each weft yarn is one fourth the usual winding speed and a length of each weft yarn equal to the preset length is measured per four weft inserting operations with the measured lengths of the weft yarns being inserted or laid down successively. The same applies to the case five or more weft yarn supply units are used. This type of weft yarn insertion is effective in cases where the weft yarns supplied from the respective weft yarn supply units are different and laid down alternately, or where the aforementioned mixing is performed for realizing a cloth of uniform quality. However, when the weft yarns of two or more kinds are used and the weft yarn lengths of the same kind are inserted successively a certain number of times, it would be necessary to provide a number of weft yarn length measurement units at least equal to said number of times for the weft yarn.
In order to avoid this deficiency, an apparatus for measuring weft yarn length has been proposed in which, in addition to the weft yarn latching pin provided to the conventional apparatus, an auxiliary latching pin is provided closer to the woven cloth than the aforementioned latching pin for controlling the transfer of the measured yarn in the weft inserting direction, thereby enabling the weft yarn of the same kind to be inserted a certain number of times in succession (Japanese Laid-open Patent Specification No. 79740/1981). In this apparatus, the weft yarns supplied from the two weft yarn supply units are wound on the winding surfaces of the respective weft yarn length measurement units at respective constant speeds. For instance, when one of the weft yarns is inserted twice in succession, after which the other yarn is inserted once, the winding speed for the former yarn is equal to two-thirds the usual winding speed, while that of the remaining weft yarn is one-third the usual winding speed.
In this pattern of weft insertion, it is assumed that, the instant one weft yarn has been released from the auxiliary latching pin and laid down, one third the preset length of the same weft yarn is latched by the latching pin on the winding surface, and that one third the preset length of the other weft yarn is latched by the associated latching pin on the associated winding surface. At the instant of the next insertion, the preset length of the former yarn is latched by the associated latching pin on the winding surface, this length of yarn being released from the latching pins and laid down. At this time, two thirds the preset length of the latter yarn is wound on the associated winding surface. At the instant of the next weft insertion, the length of the latter yarn is increased to a value necessary for one weft insertion (preset length), this length of the other yarn being then released from the latching pins and laid down. At this time, two thirds the preset length of the former yarn is stored. At the next weft insertion, a length of the former yarn necessary for the next insertion (preset length) is latched on the winding surface by the auxiliary latching pin, and one third the preset length of the same yarn is latched by the latching pins on the same winding surface. From this it follows that only one auxiliary latching pin need be provided to the length measurement unit associated with said former yarn.
When the two yarns are inserted alternately so that the same yarn is inserted twice successively, one auxiliary latching pin may be provided on each measurement unit. In this case, the winding speed for each weft yarn is equal to one half the usual winding speed.
However, in instances where the same yarn supplied from one supply unit is inserted a number of times successively, it becomes necessary to provide a plurality of said auxiliary latching pins to the measurement unit allocated to said weft yarn. For instance, supposing that one weft yarn is inserted four times successively, after which the other weft yarn is inserted thrice successively, with the winding speed for said one weft being four-sevenths of the usual speed and the winding speed for said other weft yarn being three-sevenths of the usual speed, said one weft yarn need be wound in an amount at least equal to two and two-sevenths times the preset length at the time that said one weft yarn starts to be inserted successively. This is because the length of said one yarn on the winding surface is reduced in this case to one and six-sevenths time the preset length for the second insertion, to one and three-seventh the preset length for the third insertion and to equal to said preset length for the fourth insertion. Thus a yarn length corresponding to two weft inserting operations and another yarn length corresponding to the following two weft inserting operations need be stored by two separate pairs of the auxiliary latching pins at the time that said one yarn starts to be inserted successively.
The necessity for increasing the number of auxiliary latching pins with increases in the number of times the weft yarn supplied from one supply source is inserted successively is not desirable because it gives rise to a complicated structure of the apparatus for measurement of the weft yarn. Furthermore, the above deficiency may not be removed insofar as the weft yarn is wound successively.
Thus, a demand has existed for a weft yarn length measurement apparatus whereby the weft yarn to be inserted may be freely selected without the necessity of changing mechanical parts.